Characteristics of deep levels in Al-doped ZnSe grown by molecular beam epitaxy

We investigated the characteristics of deep levels in heavily Al-doped ZnSe layers grown by molecular beam epitaxy, whose electron concentration is saturated. Low-temperature photoluminescence showed deep level emission around 2.25 eV, and its intensity increases with Al concentration. This deep-level is located at 0.55 eV above valence band maximum, implying a point defect such as a self-activated center, Al_ZnV_Zn. Deep-level transient spectroscopy was used to investigate non-radiative trap centers in Al-doped ZnSe layers, and showed the presence of two electron trap centers at depths of 0.16 and 0.80 eV below conduction band minimum, with the electron capture cross-sections of 810⁻¹² and 1×10⁻⁷ cm², respectively. It is suggested the carrier compensation in heavily Al-doped ZnSe layers be ascribed to the deep levels.